The liquid whey remaining after removal of the curd in cheese making contains about half of the nutritive materials present in the whole milk, and consists principally of a water solution of lactose (milk sugar) along with proteins (other than the casein which makes up most of the curd), together with most of the calcium, and some lipids and vitamines.
The sweet whey produced by curdling milk with rennet in preparing cured cheese can be concentrated or dried for addition to various food products, and large quantities of whey are processed in this manner.
Sour whey, produced by acidification of milk, in the preparation of cottage cheese or cream cheese, cannot be concentrated or dried satisfactorily because of its acidity, which is accentuated by concentration, because of the peculiar properties of lactic acid. Neutralizaton of the lactic acid does not solve the problem because of the resulting increase in salinity.
Sour whey not only has found no use capable of absorbing the large quantities which are produced, but has had a negative value because of the cost of finding some way to get rid of it. It cannot be used profitably as fertilizer because the cost of transportation and application to the soil is greater than its value as a fertilizer. It cannot be dumped in streams because it pollutes them. It is not even permitted to be dumped in sewers, unless a substantial fee is paid, because it increases the cost of operation of sewage treatment facilities.